Generally, a photolithography process for manufacturing semiconductor devices, and the like, employs an exposure apparatus which transfers a pattern of an original plate (e.g., a mask or a reticle) onto a photoresist-coated substrate. Recently, a projection reduction exposure apparatus advantageous for its high resolution and alignment accuracy is used as the exposure apparatus. Generally, a semiconductor device is fabricated by forming multiple layers of circuit patterns by using different original plates, on plural shot areas arrayed on the substrate.
The shot array of plural shot areas on the substrate is called a shot layout. The shot layout is made in consideration of the size of the substrate, the size of the shot area, the size of the chip area, and the like. Further, a necessary member of shots, selected based on the shot layout, for overlaying circuits for formation of the multilayer circuit, are called sample shots.
Upon selection of sample shots, an arbitrary number of shots is designated, then a determination of selectability of shots as sample shots is performed on all the shots of the shot layout, in accordance with a predetermined selectability determination condition, and a candidate shot group is determined. The selectability determination is made in consideration of the position of an alignment mark within a shot, a distance from a substrate edge of an alignment mark in each shot, a limitation due to a relative positional relation with respect to hardware mechanisms, such as an alignment mark monitoring optical system and a focus measuring system.
Next, the shots of the candidate shot group are ranked in priority order by a priority determination algorithm. In the ranking, shots in the outermost peripheral positions are often ranked to lower ordinal levels. The outermost peripheral shots are positioned on the border between an exposure area and a non-exposure area, and in comparison with inner shots, there is apprehension that the condition of an alignment mark shape, or the like, becomes unstable due to the influence of a fabrication process. When the ranking has been completed, a selection is made from high priority shots, thereby, final sample shots are selected.
Conventionally, as the shot size is smaller in comparison with the substrate size, the number of shots within the substrate is large, and the number of selectable high-priority shots as the sample shots is large. However, with a recent increase in the semiconductor device size or an increase in a one shot exposure area (angle of view), the number of shots within the substrate tends to decrease. The reduction of shots causes a reduction of shots as selection candidates upon a sample shot selection, and by extension, disturbs improvement of alignment accuracy.
The substrate size is also increased, and in such a case, the fabrication device in a fabrication plant must be changed. To enlarge a device or the angle of view of the exposure apparatus while utilizing the conventional facilities, the reduction of alignment selection candidate shots accompanying the reduction of shots within the substrate is unavoidable.
Further, regarding the alignment mark arrangement in the shot, conventionally, measurement marks are arranged in X and Y measurement directions, i.e., an X directional mark is arranged in a horizontal scribe line, and a Y directional mark is arranged in a vertical scribe line, thereby, a measurement error is suppressed to a minimum value. However, in recent years, to improve productivity, various mark arrangements are introduced. For example, a measurement mark capable of simultaneous XY directional measurement, which reduces measurement time, and an in-shot multiple point measurement mark for the purpose of correction of a shot shape are employed.
However, a necessary number of samples cannot be obtained by the conventional sample shot selection, since the number of shots is reduced, although various alignment mark arrangements have been studied. Even if the necessary number of samples can be obtained, the arrangement of shots on the substrate is not desirable.